1. Field of the Invention
The present invention relates to a photoelectric conversion device for converting an optical signal into an electric signal, and more particularly, to an image sensor IC which is a photoelectric conversion device to be applied to an image reader such as a facsimile machine or an image scanner, and a contact image sensor having one or more of the image sensor IC.
2. Description of the Related Art
Up to now, improvements have been made on a photoelectric conversion device in terms of enhancement of sensitivity and a reduction of random noise.
In order to eliminate reset noise by virtue of a circuit, as shown in FIG. 15, there has been an attempt to offset the reset noise by disposing a noise signal holding circuit.
However, according to such the conventional photoelectric conversion device, the noise signal holding circuits must be provided as many as light receiving elements, which increases a chip area. Also, in order to enhance the sensitivity of the light receiving elements, it is necessary to increase the amplification factor of a downstream signal processor circuit. However, thermal noise of the circuits other than the reset circuit is also amplified at the same time. Therefore, it is difficult to obtain the high sensitivity/noise ratio. In particular, the signal processor circuit must operate at a high-frequency read frequency, normally at the frequency of 5 MHz or higher. In this case, the noise of a high frequency band is also amplified, making it difficult to attain the high sensitivity/noise ratio.